Dental implant

ABSTRACT

Dental implant with a base body made of ceramic anchorable in a jawbone and an implant superstructure attachable to the base body using a screw, wherein in an assembled state of the dental implant, a threaded portion of the screw engages with an inner thread formed in a blind hole of the base body, wherein the implant superstructure is by the screw pressed against the base body and wherein the engagement between the threaded portion of the screw and the internal thread of the blind hole occurs only in a lower half of the base body facing away from the implant superstructure.

CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.14/085,587, filed Nov. 20, 2013, which claims benefit of the filing dateof EP12007906.6, filed Nov. 23, 2012, the entire contents of which areincorporated herein by reference for all purposes.

BACKGROUND 1. Field

The invention relates to a dental implant with a base body made ofceramic anchorable in a jawbone and an implant superstructure attachableto the base body using a screw, wherein in an assembled state of thedental implant, a threaded portion of the screw engages with an internalthread formed in a blind hole of the base body, and wherein the implantsuperstructure is by the screw pressed against the base body.

2. Description of Related Art

Such dental implants are already known from prior art. Tightening thescrew results in stresses in the material of the base body and theimplant superstructure. High stresses upon the ceramic used arise in thetightened state of the screw, both in the bearing areas between the basebody and the implant superstructure as well as around the internalthread with which the thread flanks of the screw engage. The screwconnection generates shear and tensile stresses that are particularlyharmful for ceramic materials. Consequently, the ceramic material, beingstable against compressive forces but unstable against tensile forces,is frequently overstressed. When tightening the screw, the ceramicmaterial can in the bearing area between the base body and the implantsuperstructure suffer an incipient crack or even break.

Exemplary of such prior art is EP 2 168 530 A1 which discloses a ceramicimplant comprising metallic coatings in an implant body, which areapplied on the internal thread. Such a metal layer is also applied at abevel at one end of the base body on which an implant superstructurebears in order to better absorb shear and tensile stresses. Suchmetallic inserts or coatings, however, must be applied in complexprocesses onto the ceramic base material and are therefore veryexpensive. The portion of the screw being in engagement with theinternal thread is furthermore arranged in the upper part of the basebody, whereas the lower portion of the base body is designed as a solidbody. Therefore, the stresses arising when tightening the screw areconcentrated on the upper portion of the base body, whereas no stressesprevail in the lower portion of the implant body. A multi-axial stressstate comprising tensile and shear forces is therefore concentrated inthis portion of the bearing area between the base body and the implantsuperstructure and the area around the internal thread. At the sametime, the stresses are distributed very inhomogeneously over the entirelength of the base body.

SUMMARY

The object of the present invention is to provide a dental implant thatcan be fabricated at low costs and comprises optimized transmission offorces for ceramic materials.

This object is achieved according to the invention in that theengagement between the threaded portion of the screw and the internalthread of the hole occurs only in a lower half of the base body facingaway from the implant superstructure, said lower half extending overhalf the length of the base body.

This design has the effect that the stresses generated are homogeneouslydistributed over the entire length of the base body. Furthermore, theinternal thread, into which the stresses are introduced directly via thescrew, is located far away from the contact area with the implantsuperstructure, deep at the base of the base body. Due to this largedistance between the bearing area and the portion of the internal threadengaging with the screw, tensile and shear stresses are largely avoidedin the upper half in the bearing area between the base body and theimplant superstructure. Instead, predominantly compressive stressesoccur in this area, which can be much better absorbed by the ceramicmaterial. The bearing area, frequently being thin-walled for spacereasons, between the base body and the implant superstructure is greatlyrelieved of loads and the introduction of the screw stresses at theinternal thread of the base body occurs in the more massive lower partof the base body. Consequently, the tendency to develop cracks isreduced and ease of assembly is increased. Additional reinforcement ofthe ceramic material, such as metal coatings in the bearing area and theinternal thread, is no longer necessary, whereby the manufacturing costof dental implants can be substantially reduced. It is even possible tofabricate the base body and the implant superstructure completely fromceramic without additional coatings, which again reduces manufacturingcosts. Tensile stresses therefore occur mainly in the screw. Screws madeof metal are particularly suitable for this, which in turn are cheap toproduce.

Advantageous embodiments are claimed in the dependent claims andexplained below.

It is according to a first embodiment of the invention of advantage, ifthe internal thread over its entire length extends only in the lowerhalf of the base body. It is thereby not necessary to apply a threadover the entire length of the blind hole of the base body, wherebymanufacturing costs are reduced. And shear stresses are then limitedonly to the lower part.

In a further embodiment of the invention, it is also advantageous if thelength of the blind hole amounts to at least 80%, preferably to at least90% of the total length of the base body. The entire length of the basebody is thereby used most effectively for the transmission of the screwtension.

If in a further embodiment of the invention the blind hole bore,subsequent to the internal thread in the direction of the implantsuperstructure, is embodied as a fit bore, wherein there is a clearancefit with very little play or a transition fit between the fit bore and ashank of the screw, then a simple support is provided in the transversedirection to the longitudinal axis of the screw. Shear forces arethereby easily supported by the screw shank.

It is also advantageous if the length of the fit bore is according toanother embodiment of the invention greater than the length of theinternal thread. This provides an optimal ratio between the side supportin the transverse direction and the pressure reduction in the contactarea.

According to a further embodiment of the invention, the implantsuperstructure bears against the base body at a bearing surfaceextending substantially perpendicular to the longitudinal axis of thescrew. This has the advantage that the pressure forces being transmittedby the base body to the implant superstructure or vice versa press on avertical surface, whereby stress by shear forces is avoided. An evenmore ceramic-friendly design is thereby provided.

According to an advantageous embodiment of the invention, it is alsoadvantageous if the implant superstructure comprises an extension thatis in the assembled state of the dental implant inserted into a recessof the base body. This ensures that the implant superstructure isthereby in a simple manner supported with regard to the base body in theradial direction. Radial displacement of these two parts relative toeach other is thereby prevented.

It is also possible, according to an advantageous embodiment of theinvention, to provide an anti-rotation form fit between the implantsuperstructure and the base body. Rotation of the implant superstructurerelative to the base body is prevented, in particular when being screwedtogether, but also during use.

According to a further embodiment of the invention, it is advantageousif both the implant superstructure as well as the base body are made ofceramic, preferably of zirconium oxide. This has the advantage that aparticularly strong structure of the dental implant is ensured.

If, according to a further advantageous embodiment, the implantsuperstructure and/or the base body are fabricated by powder-injectionmolding, then this enables particularly cost-effective fabrication ofthe dental implant. The internal thread can also be shaped already inthe forming process using this method, which again reduces manufacturingcosts.

The invention also provides a base body for a dental implant, which alsoprovides the advantages of low manufacturing costs and positive stressdistribution, and is universally employable for other implantsuperstructures.

The invention is explained below by means of the embodiments using thefigures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a longitudinal section of the dental implant according tothe invention along a longitudinal axis of a base body, anchored in thejaw bone of a patient, and

FIG. 2 shows a cross-section perpendicular to the longitudinal axis ofthe base body along the section line II marked in FIG. 1 as anillustrating of the anti-rotation lock.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

The figures are merely schematic in nature and serve only to understandthe invention. Same elements are denoted by the same reference numerals.

FIG. 1 shows a dental implant 1 comprising a base body 2 and an implantsuperstructure 4, which are fastened to each other using a screw 3. Adental prosthesis 5 can in turn be attached to the implantsuperstructure 4 in a known manner, for example, by cementing a dentalcrown.

The base body 2 is formed essentially cylindrically. For anchoring in ajawbone (presently not shown}, the base body 2 comprises an externalthread 6 which is introduced into a jacket area of the base body 2. Thebase body 2 is screwed into the jawbone using this external thread 6.The jacket surface tapers conically towards the lower end portion 7 ofthe base body 2 being screwed into the jaw bone, whereby screwing thebase body 2 into the jawbone is facilitated. A blind hole bore 9 isintroduced into the base body 2 from the upper end portion 8 of the basebody 2 facing away from the jaw bone and located opposite to the lowerend portion 7. The blind hole bore 9 is arranged centered in the basebody 2 and follows the longitudinal axis 10 of the base body 2 extendingfrom the upper end portion 8 to the lower end portion 7 all the way intothe lower end portion 8. The longitudinal axis 10 in the base body istherefore coaxial to the center axis of the blind hole bore 9.

Furthermore arranged at the upper end portion 8 of the base body 2 is aflat bearing surface 11 of the base body 2, which extends substantiallyperpendicular (90°) to the longitudinal axis 10 relative to thelongitudinal axis 10. Between the blind hole bore 9 and the bearingsurface 11, a recess 12 is provided in the base body 2 and co-acts withthe counter profile of an extension 24 attached to the implantsuperstructure 4 as an anti-rotation lock, as is described in moredetail below. The bearing surface 11 is the portion of the base body 2protruding farthest upwardly towards the implant superstructure 4 in thedirection of the longitudinal axis 10, and thereby forms a face side ofthe base body 2.

The distance in the direction of the longitudinal axis 10 of the basebody 2 between the bearing surface 11 and the lower face side of the endportion 7 located opposite to it is hereinafter referred to as the“length” of the base body 10. This length is divided by an imaginarydividing plane 13 in two equal halves 14, 15. In a lower half 14 of thebase body 2 facing the jawbone, an internal thread 16 is introduced intothe blind hole bore 9. The lower half 14 and the upper half 15 thereforeeach extend across half of the length of the base body 2. The blind holebore 9 extends so far into the lower half 14, that the length of theblind hole bore 9 amounts to at least 80%, particularly preferably atleast 90%, most preferably at least 95% of the total length of the basebody 2. The internal thread 16 itself is applied at an end of the blindhole bore 9 facing the lower end portion 7 and is formed only in thelower half 14 of the base body 2. Subsequent to the internal thread 16in the direction of the implant superstructure 4, still in the lowerhalf 14 of the base body 2, the internal thread 16 transitions into afit bore 17 of the blind hole bore 9. This fit bore 17 extendsend-to-end to the upper end portion of the base body 2 where the blindhole bore 9 transitions into the recess 12. The fit bore 17 is longerthan the internal thread 16.

For attaching the implant superstructure 4, the screw 3 is inserted intothe blind hole bore 9 so far until the threaded portion 18 of the screw3 can be screwed into the internal thread 16. The screw 3 is in theassembled state screwed so far into the internal thread 16, that thescrew head 19 bears against a screw head bearing 20 of the implantsuperstructure 4. The implant superstructure 4, in the assembled statebearing with a contact surface 21 against the bearing surface 11 of thebase body 2, is in this area pressed firmly against the base body 2 bytightening the screw 3. A compression stress state therefore arises inthis bearing area between the bearing surface 11 and the contact surface21.

In this assembled state, the screw 3 is with its threaded portion 18fully screwed into the internal thread 16. The threaded portion 18therefore engages completely with the internal thread 16. Since theinternal thread 16 is located entirely in the lower half 14 of the basebody 2, the engaged portion of the screw 3 is therefore located entirelyin the lower half 14 of the base body 2. A smooth shank 22 connects tothe threaded portion 18 of the screw 3 and fits into the fit bore 17 ofthe base body 2 such that a clearance fit with very little play isgiven. The fit between the shank 22 and the fit bore 17 is preferablyeven configured as a transition fit, so that slight pressure must beapplied to insert the screw 3 into the blind hole bore 9. The screw 3can thereby just barely be moved in the fit bore 17 in the direction ofthe longitudinal axis 10, but bears with the outer surface of the shank22 at least in part against the inner surface of the fit bore 17. Thecenter axis of the screw 3 is in the assembled state preferably coaxialwith the longitudinal axis 10 of the base body 2.

The shank 22 extends from the side of the screw head 19 contacting thescrew head bearing 20 to the threaded portion 18. Also, in the implantsuperstructure 4, into which the shank 22 extends in part, same isguided in a fit bore 23 of the implant superstructure 4. The fit betweenthe shank 22 and the fit bore 23 in the implant superstructure 4 isdesigned as a clearance fit with very little play. Therefore, both theimplant superstructure 4 as well as of the base body 2 are supported inthe transverse direction of the center axis of the screw 3, and, sincethis screw axis is coaxial with the longitudinal axis 10 of the basebody 2, also the base body 2 is supported in the transverse direction ofthe longitudinal axis 10.

For radial fixation of the implant superstructure 4 relative to the basebody 2, the implant superstructure 4 comprises an extension 24 that canbe inserted into the recess 12 of the base body 2. Due to the insertion,the two components are in the assembled state radially mounted andthereby supported in the transverse direction of the longitudinal axis10.

As is particularly evident from FIG. 2, the extension 24 has a certainpositive shape which is in the assembled state inserted into a negativeshape of the recess 12. An anti-rotation lock of the base body 2relative to the implant superstructure 4 about the longitudinal axis 10is thereby ensured. The profile of the extension 24 in cross-section,i.e. transverse to the longitudinal axis 10, extends substantiallyring-shaped, said ring shape comprising longitudinally extending bulges25 at its outer side facing the recess 12. These bulges 25 are arrangedon the outer side equidistantly around the center point of the extension24 defined by the longitudinal axis 10. In this embodiment, seven bulges25 are distributed uniformly around the center point, however, it isalso possible to use a different number larger or smaller than seven ofthe bulges 25 arranged in parallel to each other. The side of the recess12 facing the outer side of the extension 24 and subsequent to the blindhole bore 9 and the bearing surface 11 also extends at least in partparallel to the longitudinal axis 10 and has a negative shape that fitsto the profile of the extension 24, such that the bulges 25 engage withgrooves 26 of the recess 12. The engagement provides a support for theextension 24 at the recess 12. Any rotation of the base body 2 relativeto the implant superstructure 4 is therefore not possible.

The implant superstructure 4, being designed essentially as a hollowcylinder, comprises a customary dental prosthesis 5 at one end facingaway from the base body 2 which in the assembled state is cemented ontothe implant superstructure 4.

The base body 2 is in this embodiment made entirely of ceramic, namelyzirconium oxide, whereby the internal thread 16 at its thread flanks,which are in engagement with the threaded portion 18 of the screw 3,comprises this ceramic material. The implant superstructure 4 is alsomade entirely of ceramic material, namely zirconium oxide. Both the basebody 2 as well as the implant superstructure 4 are manufactured bypowder-injection molding, preferably using a ceramic injection molding(CIM) method.

The screw 3, or at least the shank 22 of the screw 3, is produced of asteel alloy, particularly preferably a titanium alloy.

For the assembly of the dental implant 1, the base body 2 is firstscrewed into the jawbone. If it is anchored in a sufficiently stronglymanner, preferably already grown into the bone, then the implantsuperstructure 4 is subsequently attached by screwing-in the screw 3into the bores of the implant superstructure 4 and the base body. Thescrew 3 is thereby put under tensile stress such that the implantsuperstructure 4 and the base body 2 are firmly pressed against eachother. The bearing surface 12, formed perpendicular to the longitudinalaxis 10, and the contact surface 21 bearing against it ensure surfacecontact of the implant superstructure 4 on the base body 2. Compressivestresses in the bearing area therefore occur mainly along thelongitudinal axis 10 and parallel to the center axis of the screw 3.After the screw 3 is tightened, the dental prosthesis 5 formed as acrown or a bridge is then cemented onto the implant superstructure 4.

1. Dental implant with a base body made of ceramic anchorable in ajawbone and an implant superstructure attachable to said base body usinga screw, wherein in an assembled state of said dental implant, athreaded portion of said screw engages with an inner thread formed in ablind hole of said base body, and wherein said implant superstructure isby said screw pressed against said base body wherein said engagementbetween said threaded portion of said screw and said internal thread ofsaid blind hole occurs only in a lower half of said base body facingaway from said implant superstructure.
 2. Dental implant according toclaim 1, wherein said internal thread over its entire length extendsonly in said lower half of said base body.
 3. Dental implant accordingto claim 1, wherein the length of said blind hole amounts to at least80% of the total length of said base body.
 4. Dental implant accordingto claim 1, wherein said blind hole comprises a bore, subsequent to saidinternal thread in the direction of said implant superstructure, whichis embodied as a fit bore, wherein there is a clearance fit with verylittle play or a transition fit between said fit bore and a shank ofsaid inserted screw.
 5. Dental implant according to claim 4, wherein thelength of said fit bore is greater than the length of said internalthread.
 6. Dental implant according to claim 1, wherein said implantsuperstructure bears against the base body at a bearing surfaceextending substantially perpendicular to said longitudinal axis of saidscrew.
 7. Dental implant according to claim 1, wherein said implantsuperstructure comprises an extension that is in the assembled state ofthe dental implant inserted into a recess of said base body.
 8. Dentalimplant according to claim 1, wherein there is an anti-rotation form fitbetween said implant superstructure and said base body.
 9. Dentalimplant according to claim 1, wherein both said implant superstructureas well as said base body are manufactured of ceramic material. 10.Dental implant according to claim 1, wherein both said implantsuperstructure and/or said base body is/are manufactured bypowder-injection molding methods.
 11. Base body for a dental implantaccording to claim
 1. 12. Dental implant according to claim 3, whereinthe length of said blind hole amounts to at least 90% of the totallength of said base body.
 13. Dental implant according to claim 9,wherein said ceramic material is zirconium oxide.